In an EL element, positive holes and electrons injected from counter electrodes are coupled in a light emitting layer, and fluorescent substances in the light emitting layer are excited by the energy so as to emit light of a color corresponding to the fluorescent substances. Thus, attracts an attention as a spontaneous light emitting planar display element. In particular, an organic thin film EL display, using an organic substance as a light emitting material, has high light emitting efficiency which realizes a light emission with a high brightness with a less than 10 V applied voltage, and it is capable of emitting a light by a simple element structure. Thus, application thereof to the advertisement for displaying a specific pattern by light emission and other inexpensive simple displays is expected.
In manufacturing of the display using the EL element, in general, a first electrode layer and an organic EL layer are patterned. As the method for patterning the EL element, a method of deposition of the light emitting material via a shadow mask, a method of printing by an ink jet, a method of destroying a specific light emitting dye by an ultraviolet ray irradiation, screen printing or the like can be presented. However, by these methods, it has been impossible to provide a method for manufacturing an EL element, capable of realizing all of a high light emitting efficiency, a high light taking out efficiency, manufacturing process simplicity, and a high-definition pattern formation.
As a means for solving these problems, a method for manufacturing an EL element by patterning an organic EL layer by a photolithography method has been proposed. In this method, comparing with the conventionally carried out patterning method by the vapor deposition, since vacuum equipments comprising a highly accurate alignment mechanism or the like are not needed, manufacturing can be carried out relatively easily and inexpensively. In contrast, comparing with the patterning method using the ink jet method, it is preferable in that a structure for aiding patterning or a pre-treatment to a substrate is not carried out. Furthermore, from the relationship with the discharging accuracy of an ink jet head, the method for manufacturing by the photolithography method is considered as a method more preferable for the high-definition pattern formation, and thus it is advantageous.
FIGS. 3A to 3M show a method for manufacturing an EL element having a plurality of light emitting layers by the photolithography method with these advantages. Hereinafter, FIGS. 3A to 3M will be explained.
First, as shown in FIG. 3A, a first light emitting layer 33 is formed by coating a first light emitting layer forming coating solution onto a substrate 31 having a first electrode layer 32 formed in a pattern. And further, a positive type photoresist layer 34 is formed on the first light emitting layer 33.
Next, as shown in FIG. 3B, by irradiating an ultraviolet ray 36 via a mask 35 such that only the position where the first light emitting part is formed will be a light shielding part, developing with a photoresist developing agent, and cleaning, as shown in FIG. 3C, the photoresist layer 34 remains only in the position where the first light emitting part will be formed.
Furthermore, by etching with the photoresist layer 34 formed in a pattern as a mask, as shown in FIG. 3D, the first light emitting layer 33 is etched in a pattern so as to form a first light emitting part 33′.
Next, a light emitting layer of a second color is patterned. First, as shown in FIG. 3E, a second light emitting layer forming coating solution is coated onto the substrate 31 having the first light emitting part 33′ formed in a pattern so as to form a second light emitting layer 37. Further, by coating a positive type photoresist onto the second light emitting layer 37, a second photoresist layer 34′ is formed.
As shown in FIG. 3F, the ultraviolet ray 36 is irradiated in a pattern to the second photoresist layer 34′ via the mask 35 such that the position where the first light emitting part 33′ is formed and the position where the second light emitting part will be formed will be an unexposed part. Thereafter, by developing with the photoresist developing agent, and cleaning, as shown in FIG. 3G, the second photoresist layer 34′ of the exposed part is removed so as to have the second photoresist layer 34′ remaining only in the position where the first light emitting part 33′ and the second light emitting part are formed.
Furthermore, by etching a part of the second light emitting layer 37, which is exposed by removing the second photoresist layer 34′ of the exposed part, as shown in FIG. 3H, the second light emitting layer 37 is etched in a pattern so as to form the second light emitting part 37′.
Furthermore, a light emitting layer of a third color is patterned. As shown in FIG. 3I, by coating a third light emitting layer forming coating solution, a third light emitting layer 38 is formed. And by coating a positive type photoresist on the entire surface thereof, a third photoresist layer 34″ is formed. Next, as shown in FIG. 3J, with masking the first light emitting part 33′, the second light emitting part 37′, and the parts where the third light emitting part will be formed by the photomask 35, the ultraviolet ray 36 is exposed in a pattern.
By developing the same with a photoresist developing agent and cleaning, as shown in FIG. 3K, the third photoresist layer 34″ is formed in a pattern.
Next, by etching the third light emitting layer 38, which is exposed by removing the exposed part of the third photoresist layer 34″, as shown in FIG. 3L, the third light emitting layer 38 is formed in a pattern so as to obtain a third light emitting part 38′.
Thereafter, by peeling off the unnecessary layers such as the photoresist layer laminated on each light emitting part 33′, 37′ and 38′ or the like, as shown in FIG. 3M, the patterned light emitting parts 33′, 37′ and 38′ can be obtained.
Thereafter, by forming a second electrode layer or the like on the light emitting parts 33′, 37′ and 38′, an EL element which emits the light to the downward direction in the figure can be manufactured.
However, even in the case of the photolithography method having the advantages, at the time of completing patterning of the light emitting layer and peeling off the photoresist layer, a problem may be involved in that the peeling operation cannot be carried out easily. This derives from a difficulty in selecting the photoresist peeling solution for peeling off the photoresist layer, because the solvent is limited to that satisfies the condition wherein the organic EL layer is not soluble and the photoresist layer is soluble. Also, when the contacting area of the photoresist peeling solution and the photoresist layer is small, it is difficult to exert the function of the photoresist peeling solution to the photoresist layer.
Therefore, in order to solve these problems, a method of exposing the substrate or the like to the photoresist peeling solutions for a long time or the like has been proposed. However, even when the method is employed, it is difficult to peel the photoresist layer off preferably. Moreover, in contrast, a new problem of damaging the substrate or the like is generated.